I would argue that biblically, to "believe in" is one and the same as to "have faith in". That is true in English as well as in Greek.
In reply.....to believe and to believe in basically is the same.
If I BELIEVE God,,,,I will do as He states in order to get me saved.
If I BELIEVE God...I will follow Him because I believe He is telling me the truth.
To believe means to trust....
If I believe the elevator will take me up,,,then I am trusting the elevator.
To believe in Jesus....
Means to believe in HIS NAME...
To believe in HIS AUTHORITY.
to believe in HIS CAPACITY AS GOD..
to believe He IS GOD.
If I believe Jesus,,,I trust Him as a good teacher (which is where many stop)...
If I beleive IN JESUS...then I'm trusting Him for my salvation.
We need both and I believe even in the first case I would be saved
(even though my belief system is limited).